During manufacture of many metal products, for example during manufacture of profiled metal parts or tubes, the metal is to be formed to receive the desired shape. In particular in tube mills for producing seam-welded tubes, a continuous metal strip is advanced through several work stations forming a line of work stations. In these work stations, the strip is formed to exhibit a tubular shape having an open, longitudinally extending seam formed by the abutting edges of the strip being formed. The seam is then welded and in case unwanted bead is formed a scarfing procedure may be applied for removing the bead. Obviously, during production of tubes other than seam-welded tubes, the steps of welding and subsequent scarfing can be omitted.
Tubes of various diameters and/or of different cross-sections are to be produced in the same mill, since a mill of this type comprises a number of massive precision machines representing considerable technical and financial expense. In order to be able to manufacture tubes having different diameters and/or different cross sections, different tooling is required in the line of work stations. On the other hand, since the same mill is to be used, an exchange of or a modification to the tooling of at least one work station is required to allow changeover of production from one type of tube to another type. Sometimes exchange of or modifications to the tooling of even more than one work station is required.
In the past, in order to perform the above-mentioned exchange or modification one of the ways was to shut down the production line and to remove and replace the respective tooling or to modify the mounted tooling where possible. Thereafter, the new or modified tooling had to be properly set and adjusted on the line before production could resume. The entire changeover routine could consume a considerable period of time, as much as some hours, thus resulting in a considerable expenditure in time and money. As a result, it has become necessary to maintain unduly large inventories of finished products, contrary to the current trend toward maintaining minimum inventory and frequently changing from the production of one product to another.
An alternative way was to mount the tooling for the next product to be produced “off the line”, so that production continued until the tooling for the next product was mounted and was ready for exchange. U.S. Pat. No. 5,887,472 shows an embodiment illustrating this way of changeover from production of a first product to production of a second product of different diameter or shape. In the embodiment described there, the drives of the various work stations along the line always remain in place. At the time the changeover is to be performed the production line is stopped, removable cassettes carrying the tooling are disconnected from their drives, the cassettes are removed (guided by rails in the floor) and the replacement cassettes carrying the tooling required for production of the new product are moved into their place in the production line. The new cassettes are then connected to the drives and production of the new product may start.
While this way of performing the changeover represents substantial progress with regard to efficiency, it still has some disadvantages.
Both mechanical as well as electrical disconnection and reconnection of the cassettes is comparatively complex and time consuming. In the embodiment described in the above-mentioned U.S. Pat. No. 5,887,472 the cassettes are removed with the aid of rails provided in the floor and wheels provided on the support of the cassettes, the said wheels engaging the rails thus enabling movement of the cassettes through the machine hall transverse to and along the production line. A rail system allowing such movements is very space-consuming and also the movement of the cassettes through the machine hall from and to the production line is time-consuming. In addition, movement of the cassettes from and to the production line usually occurs on the production operator's side thus disturbing continuation of the production process during preparation of a changeover.
Although not disclosed in U.S. Pat. No. 5,887,472 overhead (travelling) cranes have been used instead of rails/wheels for removing the cassettes to be replaced from the production line and for moving the new cassettes to be connected to the production line in place. Generally, an overhead crane also represents considerable expense and is often used for different purposes in the machine hall or factory, so that it may not be available at the time it is needed for the changeover of the cassettes. Sometimes, an overhead crane is not available at all. More importantly, however, an overhead crane only allows one cassette at a time to be carried from or to the production line, so that the cassettes can only be exchanged one after another. Accordingly, replacement of the cassettes using an overhead crane is rather time-consuming.
Taking these disadvantages into account, it is an object of the instant invention to suggest an improved changeover system.